//第四章
// 2、Shape接口和它的两个实现类
interface Shape {
    double area(double givenValue);
}

/*
//Square类
class Square implements  Shape{

    public double area(double sideLength){
        return sideLength*sideLength;
    }
}
//Circle类
 class Circle implements Shape{
        public double area(double r){
            return  Math.PI * r * r;

        }
    }

 */